EGG SIZE PLASTICITY IN A SEED BEETLE - AN ADAPTIVE MATERNAL EFFECT

ln the seed beetle, Staler limbatus, the fitness consequences of egg s ize vary substantially among host plants. There is intense selection f or laying large eggs when larvae will develop on seeds of Cercidium fl oridum (caused by high mortality penetrating the seed coat) but select ion for laying small eggs when larvae will develop on seeds of Acacia greggii (caused by very low mortality penetrating the seed coat and an egg size/egg number trade-off). We test the hypothesis that host-asso ciated variation in egg size within populations of S. limbatus represe nts an adaptive maternal effect in which females adjust egg size in re sponse to host species. In laboratory experiments, S. limbatus females laid significantly larger and fewer eggs on C. floridum than on A. gr eggii. When switched between hosts, females readjusted egg size, produ cing progressively larger eggs on C. floridum and smaller eggs on A. g reggii. When conditioned to lay either small eggs (on A. greggii) or l arge eggs (on C. floridum), and then forced to lay on C. floridum, fem ales conditioned on C. floridum laid eggs that had substantially highe r survivorship than eggs laid by females conditioned on A. greggii, Th ese experiments demonstrate that egg size is an adaptively plastic cha racter in S. limbatus.